Physics MCQ Quiz - Objective Question with Answer for Physics - Download Free PDF

The correct answer is Electric heater.

Key Points

• An electric heater works by converting electrical energy into heat energy using resistive heating elements.
• It does not rely on the interaction of a current-carrying conductor with a magnetic field to generate heat.
• Electric motors use current-carrying conductors in magnetic fields to produce mechanical motion.
• Electric fans use electric motors, which in turn use current-carrying conductors in magnetic fields to operate.
• Electric generators convert mechanical energy into electrical energy through the use of current-carrying conductors in magnetic fields.

Additional Information

• Electric Motor
  • It operates on the principle of the Lorentz force, where a current-carrying conductor in a magnetic field experiences a force.
  • Used in various applications including fans, pumps, and household appliances.
• Electric Generator
  • Works on the principle of electromagnetic induction, where a conductor moving in a magnetic field induces an electromotive force (EMF).
  • Commonly used to provide power in places without access to the electrical grid.
• Electric Fan
  • Uses an electric motor to convert electrical energy into mechanical energy, causing the blades to rotate and move air.
  • Electric fans are widely used for cooling and ventilation purposes.

The correct answer is Convex, concave.

Key Points

• A convex lens is thicker at the center and converges light rays to a focal point. It is also known as a converging lens.
• A concave lens is thinner at the center and diverges light rays outward. It is also called a diverging lens.
• Convex lenses are commonly used in applications such as magnifying glasses, cameras, and eyeglasses for farsightedness.
• Concave lenses are used in devices like binoculars, telescopes, and eyeglasses for nearsightedness.
• The behavior of light through these lenses is governed by the principles of refraction, where the bending of light occurs at the lens surfaces.

Additional Information

• Focal Point: The focal point is the point where light rays either converge (convex lens) or appear to diverge from (concave lens).
• Lens Formula: The relationship between the focal length (f), object distance (u), and image distance (v) is given by 1/f = 1/v - 1/u.
• Power of a Lens: The power of a lens is measured in diopters (D) and is calculated as P = 100/f, where f is the focal length in centimeters.
• Types of Lenses: Lenses are classified as convex, concave, and cylindrical, depending on their shape and function.
• Applications: Lenses play critical roles in optical instruments, including microscopes, telescopes, cameras, and corrective eyewear.

The correct answer is Lemon Juice.

Key Points

• Lemon juice conducts electricity because it contains citric acid, which dissociates into ions in solution.
• The presence of free ions such as hydrogen (H⁺) and citrate ions enables the flow of electric current.
• Compared to distilled water, vegetable oil, and milk, lemon juice has a higher concentration of electrolytes, making it a better conductor.
• Distilled water lacks dissolved ions, while vegetable oil is a non-polar substance and does not dissociate into ions.
• Milk contains some ions but its conductivity is lower than that of lemon juice because its ion concentration is relatively lower.

Additional Information

• Electrolytes:
  • Substances that dissolve in water to produce ions, enabling the conduction of electricity.
  • Examples include salts (like NaCl), acids (like HCl), and bases (like NaOH).
• Non-Electrolytes:
  • Substances that do not produce ions when dissolved in water and do not conduct electricity.
  • Examples include pure water, sugar, and oils.
• Distilled Water:
  • It is purified water that lacks dissolved ions, making it a poor conductor of electricity.
• Conductivity of Milk:
  • Milk contains dissolved salts and minerals such as calcium and potassium ions, making it a weak conductor compared to electrolytic solutions like lemon juice.
• Polarity of Vegetable Oil:
  • Vegetable oil is a non-polar substance, meaning it does not ionize or conduct electricity in its natural state.

The correct answer is Statement I and III are correct.

Key Points

• Statement I: The frequency of vibration determines the pitch of the sound. This statement is correct as the pitch is directly related to the frequency of the sound wave; higher frequency results in higher pitch.
• Statement II: A higher frequency of vibration produces a lower pitch. This statement is incorrect as higher frequency corresponds to a higher pitch.
• Statement III: Amplitude affects the loudness of the sound. This statement is correct as the loudness of a sound is determined by its amplitude; higher amplitude results in louder sound.

Additional Information

• Pitch: The perceived frequency of a sound; it is how high or low a sound seems to a listener.
• Frequency: The number of vibrations or cycles per second of a sound wave, measured in Hertz (Hz).
• Amplitude: The height of the sound wave, which determines the loudness or volume of the sound.
• Loudness: A subjective perception of sound pressure, influenced by the amplitude of the sound wave.
• Sound waves are characterized by their wavelength, frequency, amplitude, and speed, which together determine the sound's pitch, loudness, and quality.

The correct answer is Both Assertion and Reason are correct, and Reason is the correct explanation for Assertion.

Key Points

• Pressure is defined as the force applied per unit area, mathematically expressed as Pressure = Force/Area.
• The assertion correctly states that pressure is inversely proportional to the area on which a force is applied. As the area decreases, pressure increases and vice versa.
• The reason explains the relationship effectively: a smaller area concentrates the force over a smaller surface, leading to higher pressure.
• This principle is applied in real-life scenarios, such as sharp objects (e.g., knives or needles) exerting high pressure due to their small contact area.
• Both the assertion and reason align with fundamental concepts in physics, making the reason a valid explanation for the assertion.

Additional Information

• Pressure: A scalar quantity measured in Pascal (Pa), where 1 Pascal = 1 N/m².
• Force: A vector quantity responsible for causing motion or deformation in an object. It is measured in Newtons (N).
• Applications of Pressure:
  • Hydraulic systems (e.g., car brakes) utilize pressure to transmit force through fluids.
  • Snowshoes distribute weight over a larger area, reducing pressure and preventing sinking into snow.
• Real-world examples: High-pressure areas in weather systems lead to clear skies, while low-pressure areas result in storms.
• Concept of Inverse Proportionality: Inverse proportionality describes a relationship where one variable increases while the other decreases, commonly observed in physics and mathematics.

CONCEPT:

• Wave: The disturbance that transfers energy from one place to another is called a wave.

There are mainly two types of waves:

1. Transverse waves: The wave in which the movement of the particles is at right angles to the motion of the energy is called a transverse wave. Light is an example of a transverse wave.
2. Longitudinal wave: The wave in which the movement of the particles is parallel to the motion of the energy is called a longitudinal wave. The sound wave is an example of a longitudinal wave.

EXPLANATION:

• Light-wave is a transverse wave because its components vibrate perpendicular to its direction of propagation. So option 1 is correct.

The correct answer is Newton's first law.

Key Points

• Newton's laws of motion-
  • ​Newton’s first law states that, if a body is at rest or moving at a constant speed in a straight line, it will remain at rest or keep moving in a straight line at constant speed unless it is acted upon by force.
    • This postulate is known as the law of inertia. The law of inertia was first formulated by Galileo Galilei for horizontal motion on Earth and was later generalized by René Descartes.
    • Before Galileo, it had been thought that all horizontal motion required a direct cause. Still, Galileo deduced from his experiments that a body in motion would remain in motion unless a force (such as friction) caused it to come to rest.
  • Newton’s second law is a quantitative description of the changes that a force can produce in a body's motion.
    • It states that the time rate of change of a body's momentum is equal in both magnitude and direction to the force imposed on it.
    • The momentum of a body is equal to the product of its mass and its velocity. Momentum, like velocity, is a vector quantity, having both magnitude and direction.
    • A force applied to a body can change the magnitude of the momentum, direction, or both.
    • For a body whose mass m is constant, it can be written in F = ma, where F (force) and an (acceleration) are vector quantities.
    • If a body has a net force acting on it, it is accelerated by the equation. Conversely, if a body is not accelerated, there is no net force acting on it.
  • Newton’s third law states that when two bodies interact, they apply forces to one another that are equal in magnitude and opposite in direction.
  • The third law is also known as the law of action and reaction. This law is important in analyzing static equilibrium problems, where all forces are balanced, but it also applies to bodies in uniform or accelerated motion.
  • The forces it describes are real ones, not mere bookkeeping devices. For example, a book resting on a table applies a downward force equal to its weight on the table.
  • According to the third law, the table applies an equal and opposite force to the book. This force occurs because the book's weight causes the table to deform slightly so that it pushes back on the book like a coiled spring.

The correct answer is At the centre of the Earth.

• The centre of the Earth is such that if we are at that place, the mass around us can be considered to be condensed at the surface of the Earth itself, i.e considering the Earth as a spherical shell.
• Inside a spherical shell, there is no change in potential as one moves inside, and since only a change in potential implies a force there is no force.
• Hence the acceleration due to gravity is zero at the centre of the Earth.

The correct answer is Gamma Rays.

Key Points

• Gamma rays have the shortest wavelength and highest frequency (energy) in the electromagnetic spectrum.
• They are electromagnetic waves with wavelengths in the range of 10^-12m and frequencies around 10²⁰- 10²⁴ Hz.
• They have a high penetrating power.
• They are a result of decaying radioactive material and can also be found in outer space.
• They are used in medical applications for sterilisation of equipment and cancer treatment.

Additional Information

•  Other radiations in the Electromagnetic spectrum are:

The correct answer is 342 m.

CONCEPT:

• Echo: If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.
  • Echoes are heard due to the phenomenon of Reflection of sound waves.
  • To hear the echo clearly, the reflecting object must be more than 17.2 m from the sound source for the echo to be heard by a person standing at the source.

CALCULATION:

Speed of sound = 342 m/s.

The time is taken for hearing an echo = 2s.​

• The speed of sound is

\(⇒ Speed (v)= \frac{distance (d)}{time (t)}\)

Distance travelled = 2d = v × t

⇒ 2 × d = 342 × 2

⇒ d = (342 × 2)/2

The correct answer is the Microwave.

Key Points

• A microwave oven uses microwaves to heat food.
• In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz).
• Radio waves in this frequency range absorbed by water, fats, and sugars. When they are absorbed they are converted directly into atomic motion or vibration.
• Therefore heavy motion or vibration is converted into heat.

Important Points

• Microwaves are not absorbed by most plastics, glass, or ceramics.
• The frequency of the Microwave equals the resonance frequency of water. Therefore foods could be heated up by the oscillation of water molecules.

Additional Information

• An Electric heater, Electric blub (with filament), Electric iron is the electrical device that converts an electric current into heat.
• They working on the principle of the Joule heating effect.
  • An electric current passing through a resistor will convert that electrical energy into heat energy.

The correct answer is 12250 W.

Concept:

• Power: Power is the amount of energy transferred or converted per unit time.
  • The unit of power is watt or J/s.
  • Its dimensional formula is: [M L² T^-3].

Calculation:

Given: v = 700 m/s, m = 50 g = 0.05 kg, n/t = 60 bullets/min ⇒  1 bullet/s

The power developed by the gun is given by formula -

Power = Work done / time = Energy consumed / time

\(Power = n \times \frac{{\frac{1}{2}m{v^2}}}{t}\)

\(Power = \frac{n}{t}\; \times \frac{1}{2}m{v^2}\)

\(Power = 1 \times \frac{1}{2} \times 0.05 \times {700^2}\)

Power = 12250 watt

Calculations:

Given,

Distance of the object from the lens = u = -10 cm

Refractive index of the lens = µ = 1.5

The Radii of curvature of the lens are 20 cm in magnitude

R₁ = 20 cm and R₂ = -20 cm          (As per sign convention)

According to Len's Maker's formula

\(\frac{1}{f}=(\mu - 1)(\frac{1}{R_1}-\frac{1}{R_2})=(1.5-1)(\frac{1}{20}-\frac{1}{-20})\\ =0.5 \times \frac{2}{20}=\frac{1}{20}\\ or, \; f=20 \; cm \)

From the Lens equation,

\(\frac{1}{v}-\frac{1}{u}=\frac{1}{f}\\ \frac{1}{v}=\frac{1}{f}+\frac{1}{u}\\ or, \; v=\frac{fu}{u+f}=\frac{20 \times (-10)}{-10+20}=\frac{-200}{10}=-20 \; cm\)

The image is formed 20 cm on the same side as the object.

The correct answer is 10-4 microns.

Key Points

Read the question ,it is asking value  in microns not meter.

If asked in meters then the value will be 1 Angstroms  = 10^-10 m.

But asked in microns

• 1 mm = 10^-3 m
• 1 micron = 10^-3 mm
  • ⇒ 1 micron = 10-6 m
• 1 Angstrom = 10^-10 m
  • 1 Angstrom = 10-10 m = 10-10 × 106 micron = 10-4 micron.

Confusion Points

1 Angstrom = 10^-10 meter

1 Angstrom =  10^-4 micron

Additional Information

• An Angstrom is a unit of length used to measure very small distances.
• 1 Angstroms to = 0.0001 Microns 
• It is named after Anders Jonas Ångström (Swedish physicist).
• A micron is one-millionth of a meter (10−6 m) and one Angstrom is 10-4 micron.

The correct answer is Ohm.

Key Points

• Impedance is the total sum of resistance and reactance.
• The SI Unit of Impedance(Z), resistance(R), and reactance(X) is Ohm(Ω).
• Reactance is a kind of imaginary resistance offered by electrical components like Capacitance and Inductor.
  • Reactance offered by the Inductor is called Inductive reactance, given as X_L = 2πfL.
  • Reactance offered by the Capacitor is called Capacitor reactance, given as  \(X_{C}=\frac{1}{2\pi fC}\).
  • Where 'f' - frequency of the source, 'L' - Inductance, and 'C' - Capacitance.

Additional Information